[structure applied to a photolithographic process and method for fabricating a semiconductor device]

ABSTRACT

A structure applied to a photolithographic process is provided. The structure comprises at least a film layer, an optical isolation layer, an anti-reflection coating and a photoresist layer sequentially formed over a substrate. In the photolithographic process, the optical isolation layer stops light from penetrating down to the film layer. Since the optical isolation layer is set up underneath the photoresist layer, light emitted from a light source during photo-exposure is prevented from reflecting from the substrate surface after passing through the film layer. Thus, the critical dimensions of the photolithographic process are unaffected by any change in the thickness of the film layer.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention relates to a structure applied to aphotolithographic process and a method for fabricating a semiconductordevice. More particularly, the present invention relates to a structureapplied to a photolithographic process for improving critical dimensionsuniformity and a method that utilizes the structure to fabricate asemiconductor device.

2. Description of the Related Art

In the fabrication of a semiconductor device, a number ofphotolithographic processes needs to be carried out. Since eachphotolithographic process is going to affect the final quality of thesemiconductor device, photolithography is a very important process. Forexample, accuracy of the photolithographic process is a major factorthat determines the highest possible circuit density and the ultimatereliability of an integrated circuit. Furthermore, the photolithographicprocess affects the positioning and uniformity of metallic interconnectsand via plugs connection with transistor significantly.

However, in a conventional photolithographic process, the photoresistlayer can hardly absorb all light emitted from the photo-exposure lightsource. Consequently, a portion of the incoming light will penetratethrough the photoresist layer and reflect from the substrate. Theincoming light may interfere constructive or destructively with thereflected light to produce standing waves. Under such circumstances, theprofile of the photoresist layer after photoresist patterning will befuzzy.

To resolve the back reflection problem, an anti-reflection coating isformed underneath the photoresist layer (that is, form ananti-reflection layer between the photoresist layer and an underlyingfilm layer) to absorb the light that penetrates through the photoresistlayer during a photo-exposure. In the presence of the anti-reflectioncoating, interference between incoming and reflected light is minimized.In general, the anti-reflection coating is fabricated using a dielectricmaterial such as silicon nitride, silicon oxynitride or an organicmaterial with high light absorption properties.

However, the light absorption coefficients of all these materials areoften insufficiently high to absorb most of the incoming light. In otherwords, a portion of the incoming light still penetrates through theanti-reflection coating and underlying film layers and gets reflected bythe substrate surface to interfere with the incoming light. Moreover,the critical dimensions of a photoresist pattern are often affected byany varying of thickness in the film layer underneath theanti-reflection coating. Ultimately, critical dimensions of thephotoresist pattern will not be uniform.

SUMMARY OF INVENTION

Accordingly, at least one objective of the present invention is toprovide structure applied to a photolithographic process for stoppinglight emitted from a light source during a photo-exposure frompenetrating through a film layer to reach a substrate surface. Hence,variation in the thickness of the film layer has very little effect onthe critical dimensions of the photolithographic process.

At least a second objective of this invention is to provide a method offabricating a semiconductor device that deploys the aforementionedphotolithographic processing structure so that the device can havehighly uniform critical dimensions.

To achieve these and other advantages and in accordance with the purposeof the invention, as embodied and broadly described herein, theinvention provides a structure applied to a photolithographic process.The structure comprises a substrate having at least a film layerthereon. Furthermore, an optical isolation layer, an anti-reflectioncoating and a photoresist layer are set up over the substratesequentially. The optical isolation layer stops incoming light frompenetrating through the layer. In one embodiment, the optical isolationlayer has a light absorbing coefficient larger than 1.8. Hence, theamount of light that can reach the surface of the substrate during aphoto-exposure process is greatly reduced.

This invention also provides a method of fabricating a semiconductordevice. First, a substrate is provided. Thereafter, at least a filmlayer, an optical isolation layer, an anti-reflection coating and aphotoresist layer are sequentially formed over the substrate. Aphotolithographic process is carried out to pattern the photoresistlayer so that a portion of the anti-reflecting coating is exposed. Usingthe patterned photoresist layer as a mask, the anti-reflection coatingand the optical isolation layer are patterned and openings are formed inthe film layer above the substrate.

This invention also provides an alternative method of fabricating asemiconductor device. First, a substrate having at least a film layer,an optical isolation layer, an anti-reflection coating and a photoresistlayer already sequentially formed thereon is provided. Thereafter, aphotolithographic process is carried out to pattern the photoresistlayer so that a portion of the anti-reflecting coating is exposed. Usingthe patterned photoresist layer as a mask, the anti-reflection coatingand the optical isolation layer are patterned. The patterned photoresistlayer and the patterned anti-reflection coating are removed. Finally,using the optical isolation layer as a mask, an etching operation iscarried out to form openings in the film layer.

In the aforementioned photolithographic processing structure, an opticalisolation layer is set up underneath the photoresist layer. Hence,during photo-exposure, light from a light source can hardly penetratethrough the film layer to get a back reflection from the substratesurface. In other words, thickness of the film layer underneath thephotoresist layer has very little effect on the critical dimensions ofthe photolithographic process.

In addition, critical dimensions of the semiconductor device insubsequent fabrication process will improve due to a better control ofthe critical dimensions during the photolithographic process.Furthermore, the optical isolation layer in the aforementioned structuremay serve as an etching stop layer or a polishing stop layer as well.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIGS. 1A through 1E are schematic cross-sectional views showing theprogression of steps for forming the contacts of metallic interconnectsaccording to a first preferred embodiment of this invention.

FIGS. 2A and 2B are schematic cross-sectional views showing a portion ofthe steps for producing the contacts of metallic interconnects accordingto another preferred embodiment of this invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts.

In the following description, the process of fabricating the contacts ofmetallic interconnects is used as an example to show how the structureof this invention can be applied to a photolithographic process.

FIGS. 1A through 1E are schematic cross-sectional views showing theprogression of steps for forming the contacts of metallic interconnectsaccording to a first preferred embodiment of this invention. As shown inFIG. 1A, a dielectric layer 102, an optical isolation layer 104, ananti-reflection coating 106 and a photoresist layer 108 are sequentiallyformed over a substrate 100. The dielectric layer 102 serves as aninter-layer dielectric layer for the metallic interconnects and covers aplurality of semiconductor devices (not shown) and other film layers(not shown) already formed on the substrate 100.

The optical isolation layer 104 preferably has a light absorbingcoefficient greater than 1.8. Furthermore, the optical isolation layer104 is fabricated using a metallic material or a conductive materialincluding polysilicon, tungsten or aluminum, for example. Theanti-reflection coating 106 is fabricated using an inorganic materialsuch as silicon nitride or silicon oxynitride or an organic materialsuitable for anti-reflection.

As shown in FIG. 1B, a photolithographic process is carried out topattern the photoresist layer 108 into a patterned photoresist layer 108a so that a portion of the anti-reflection coating 106 is exposed.

Note that the anti-reflecting coating 106 is able to absorb some of thelight passing through the photoresist layer 108 during thephoto-exposure in the photolithographic process. Any residual light notabsorbed by the anti-reflection coating 106 is completely blocked by theoptical isolation layer 104. The optical isolation layer 104 has a highlight absorption coefficient so that most of the light passing throughthe anti-reflection coating 106 is absorbed. Furthermore, the opticalisolation layer 104 reflects a portion of the light back onto theanti-reflection coating 106 so that the anti-reflection coating 106 canreabsorb the light. As a result, the optical isolation layer 104 is ableto block any light heading towards the underlying dielectric layer 102.Consequently, any variation in thickness of the dielectric layer 102underneath the photoresist layer 108 has little effect on the criticaldimensions of the photolithographic process. That means, the criticaldimensions produced after the photolithographic process is highlyuniform.

Aside from blocking the passage of light, the optical isolation layer104 may serve as an etching stop layer or a polishing stop layer in asubsequent process. Details of its application are explained below.

As shown in FIG. 1C, an etching process is carried out using thepatterned photoresist layer 108 a as a mask to form a patternedanti-reflection coating 106 a, an optical isolation layer 104 a and aplurality of contact openings 110 in the dielectric layer 102.

Note that a definite thickness of the patterned photoresist layer 108 a,the anti-reflection coating 106 a or the entire patterned photoresistlayer 108 a and the anti-reflection coating 106 a may be etched awayafter the etching operation. However, because the optical isolationlayer 104 is fabricated using a metallic or polysilicon material in thisinvention, the dielectric layer has an etching rate much higher than theoptical isolation layer 104. Even though the patterned photoresist layer108 a and the patterned anti-reflection coating 106 a are completelyetched away, the optical isolation layer 104 a can still serve as anetching mask to complete the patterning process and form the contactopenings 110 in the dielectric layer 102.

As shown in FIG. 1D, the patterned photoresist layer 108 a and thepatterned anti-reflection coating 106 a are removed. If the patternedanti-reflection coating 106 a is fabricated using organic material, thepatterned anti-reflection coating 106 a and the photoresist layer 108 acan be removed together in the same process. However, if the patternedanti-reflection coating 106 a is fabricated using inorganic materialsuch as silicon nitride or silicon oxynitride, a separate etchingprocess must be carried out after removing the photoresist. Thereafter,a material layer 112 is formed over the patterned optical isolationlayer 104 a so that the contact openings 110 are completely filled. Thematerial layer 112 is fabricated using a metallic material such astungsten, copper or a conductive material.

As shown in FIG. 1E, a chemical-mechanical polishing process is carriedout to remove the material layer 112 above the patterned opticalisolation layer 104 a and expose the optical isolation layer 104 a.Hence, contacts 114 are formed in the dielectric layer 102. Note thatthe patterned optical isolation layer 104 a can serve as a polishingstop layer in the chemical-mechanical polishing process.

If the contact openings 110 have a high aspect ratio, another series ofstep may be performed to form the contact openings 110 after patterningthe photoresist layer 108 a (as shown in FIG. 1B). The method isexplained as another embodiment of this invention below.

FIGS. 2A and 2B are schematic cross-sectional views showing a portion ofthe steps for producing the contacts of metallic interconnects accordingto another preferred embodiment of this invention. As shown in FIG. 2A,after forming the patterned photoresist layer 108 a as shown in FIG. 1B,an etching operation is carried out using the patterned photoresistlayer 108 a as a mask to form a patterned anti-reflection coating 106 aand a patterned optical isolation layer 104 a.

As shown in FIG. 2B, the patterned photoresist layer 108 a and thepatterned anti-reflection coating 106 a are removed. Thereafter, usingthe patterned optical isolation layer 104 a as a mask, an etchingoperation is carried out to form contact openings 110 in the dielectriclayer 102. Since the patterned photoresist layer 108 a and the patternedanti-reflection coating 106 a are removed before etching the dielectriclayer 102, the aspect ratio of the contact openings 110 is greatlyreduced. Hence, the contact openings 110 are easier to form.

After forming the contact openings 110, conductive material is depositedinto the contact openings 110 to form the contact as in the firstembodiment (refer to FIGS. 1D and 1E).

Since the optical isolation layer effectively stops any light from goingto the film layer underneath, any variation of thickness of the filmlayer underneath the photoresist layer will not affect the criticaldimensions of the photolithographic process. Furthermore, the opticalisolation layer may serve as a stopping layer in a subsequentchemical-mechanical polishing process or an etching process.

Although the process of fabricating the contacts of metallicinterconnects is used in the two aforementioned embodiments, theapplications of the photolithographic processing structure according tothis invention are not limited as such. In fact, any photolithographicprocess for fabricating a semiconductor device may utilize the structureto improve the uniformity of critical dimensions.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1-6. (canceled)
 7. A method of fabricating a semiconductor device,comprising the steps of: providing a substrate having at least a filmlayer, an optical isolation layer, an anti-reflection coating and aphotoresist layer sequentially formed thereon, wherein the opticalisolation layer has a light absorption coefficient sufficient to blocklight through the anti-reflection coating incident thereon; performing aphotolithographic process to pattern the photoresist layer so that aportion of the anti-reflection coating is exposed; and patterning theanti-reflection coating, the optical isolation layer and the film layerto form an opening in the film layer.
 8. The method of claim 7, whereinthe step for pattering the anti-reflection coating, the opticalisolation layer and the film layer comprises performing an etchingoperation using the patterned photoresist layer as a mask in which thefilm layer has an etching rate greater than the optical isolation layer.9. The method of claim 8, wherein the patterned photoresist layer andthe patterned anti-reflection coating are also removed in the etchingoperation.
 10. A method of fabricating a semiconductor device,comprising the steps of: providing a substrate having at least a filmlayer, an optical isolation layer, an anti-reflection coating and aphotoresist layer sequentially formed thereon; performing aphotolithographic process to pattern the photoresist layer so that aportion of the anti-reflection coating is exposed; performing an etchingoption using the patterned photoresist layer as a mask to pattern theanti-reflection coating, the optical isolation layer and the film layerto form an opening in the film layer, wherein the film layer has anetching rate greater than the optical isolation layer; removing thepatterned photoresist layer and the anti-reflection coating; forming amaterial layer over the substrate covering the optical isolation layerand completely filling the opening; and performing a chemical-mechanicalpolishing operation using the optical isolation layer as a polishingstop layer to remove the material layer over the optical isolationlayer. 11-16. (canceled)
 17. The method of claim 7, wherein afterforming the opening, the method further comprises: removing thepatterned photoresist layer and the anti-reflection coating; forming amaterial layer over the substrate covering the optical isolation layerand completely filling the opening; and performing a chemical-mechanicalpolishing operation using the optical isolation layer as a polishingstop layer to remove the material layer over the optical isolationlayer.
 18. The method of claim 7, wherein the optical isolation layerhas a light absorption coefficient greater than 1.8.
 19. The method ofclaim 7, wherein the optical isolation layer comprises a conductivelayer.
 20. The method of claim 7, wherein the optical isolation layercomprises a metallic layer.
 21. The method of claim 7, wherein theoptical isolation layer comprises an organic layer.
 22. The method ofclaim 7, wherein the optical isolation layer comprises an inorganiclayer.
 23. The method of claim 10, wherein the optical isolation layerhas a light absorption coefficient greater than 1.8.
 24. The method ofclaim 10, wherein the optical isolation layer comprises a conductivelayer.
 25. The method of claim 10, wherein the optical isolation layercomprises a metallic layer.
 26. The method of claim 10, wherein theoptical isolation layer comprises an organic layer.
 27. The method ofclaim 10, wherein the optical isolation layer comprises an inorganiclayer.
 28. A method of fabricating a semiconductor device, comprisingthe steps of: providing a substrate having at least a film layer, anoptical isolation layer, an anti-reflection coating and a photoresistlayer sequentially formed thereon, wherein the optical isolation layerhas a light absorption coefficient greater than 1.8; performing aphotolithographic process to pattern the photoresist layer so that aportion of the anti-reflection coating is exposed; and patterning theanti-reflection coating, the optical isolation layer and the film layerto form an opening in the film layer.
 29. The method of claim 28,wherein the step for patterning the anti-reflection coating, the opticalisolation layer and the film layer comprises performing an etchingoperation using the patterned photoresist layer as a mask in which thefilm layer has an etching rate greater than the optical isolation layer.30. The method of claim 28, wherein after forming the opening, themethod further comprises: removing the patterned photoresist layer andthe anti-reflection coating; forming a material layer over the substratecovering the optical isolation layer and completely filling the opening;and performing a chemical-mechanical polishing operation using theoptical isolation layer as a polishing stop layer to remove the materiallayer over the optical isolation layer.
 31. The method of claim 28,wherein the optical isolation layer comprises a conductive layer. 32.The method of claim 28, wherein the optical isolation layer comprises ametallic layer.
 33. The method of claim 28, wherein the opticalisolation layer comprises an organic layer.
 34. The method of claim 28,wherein the optical isolation layer comprises an inorganic layer.